1. Field of the Invention
The present invention relates to a disk cartridge including a cartridge casing rotatably accommodating a recording medium disk, e.g. a magnetic disk, a photo disk, or a photo-magnetic disk. It also relates to a shutter made of a synthetic resin for opening and closing a read/write window formed in the cartridge casing. The present invention further relates to a manufacturing apparatus for the shutter and a manufacturing method thereof.
2. Discussion of Related Art
A disk cartridge shown in FIG. 22 is known as a one of such cartridge disk. The disk cartridge shown in FIG. 22 comprises a cartridge casing 1 formed by combining two casing halves 1a and 1b together, both made of synthetic resin, and a flexible magnetic disk 2 rotatably accommodated in the casing 1. The magnetic disk 2 is provided at a center portion thereof with a hub 3. The hub 3 is exposed through an opening 4 formed at a center of the cartridge casing 1. A driving apparatus rotates the magnetic disk 2 at a pre-determined rotating speed through the hub 3.
The cartridge casing 1 is provided at opposite sides thereof with rectangular recess portions 6. Read/ write windows 5 are formed in the recess portions 6, into which a magnetic head enters. A shutter 7 of a U-shaped cross section rides slidably astride the recess portions 6.
The shutter 7 comprises two side plates 9a, 9b and a connecting member 10 for connecting one ends of the side plates 9a, 9b. The shutter 7 further comprises a rectangular head access hole 8 of the substantially the same dimension and shape as that of the window 5. The shutter 7 is elastically urged by a spring member accommodated therein (not shown) so as to close the windows 5. On the contrary, if the shutter 7 is moved against the force of the spring member to abut on the stepped part of the recess portion 6, the access hole 8 aligns with the windows 5 to open them, thereby permitting the magnetic head to access the magnetic disk 2.
The shutter is made of a metal material or synthetic resin. The metal shutter may shave down sliding surfaces of the recess portions 6 by edge portions of the shutter 7 on sliding movement of the shutter 7 to provide shavings of the synthetic resin casing 1. The shavings may adhere to the surfaces of the magnetic disk 2 to readily cause recording and reproducing errors. In order to prevent such errors, the clearance is increased between the cartridge casing 1 and the shutter 7. In this case, foreign substance easily enters from the outside into the casing 1 through the clearance. Accordingly, foreign substances will adhere to the magnetic disk surfaces to also cause recording and reproducing errors.
On the contrary, the synthetic resin shutter can eliminate the problem pertaining to the shavings. Accordingly, it is possible that the shutter 7 is so moulded as to closely and elastically ride astride the recess portions 6, thereby preventing the foreign substances from entering into the casing 1 through the shutter portion.
The shutter 7 is made by the manufacturing apparatus shown in FIGS. 23 and 24. The manufacturing apparatus includes a stationary mould 11, a pair of side slide moulds 12, a core 13 to be disposed between the side slide moulds 12 and 12, a pair of side locks 14, a cavity 15 for the shutter and an ejecting pin 16 slidably disposed in the core 13. The letter Z designates the mould clamping direction.
In FIG. 23, the stationary mould 11, the side slide moulds 12, and the core 13 are clamped together as to define the cavity 15 in the moulding operation. The side slide mould 12 abuts at a tapered portion 12a thereof against a tapered portion 14a of the slide lock 14 to clamp the moulds together under an appropriate clamping force.
The moulds are held with a clamping force being applied thereto in the direction Z, and the synthetic resin is injected into the cavity 15 by means of an injection means (not shown) to provide the mouldings. After cooling of the mouldings, the side slide moulds 12, 12 are separated from each other. The moulded shutter 7 mounted on the core 13 is ejected therefrom by means of the ejecting pin 16.
In this conventional manufacturing apparatus, the force applied to each slide lock 14 and 14 may be ununiform, or abutting force against the core 13 from one side slide mould 12 may differ from that from the other side slide mould 12 due to dispersion of manufacturing accuracy. If the abutting forces differ from each other, since the core 13 is thin (about 2.8 mm), the core 13 may incline towards either side thereof As a result, the side plates 9a and 9b of the shutter 7 differ from each other in the thickness thereof. Further, the molten resin enters between the side slide mould 12 and the core 13, which are abutted to each other, with a lower abutting force to provide the mouldings with moulding flash.
Further, the core 13 is provided therein with a small straight bore for the ejecting pin 16. The core has, for example, a thickness of about 2.8 mm and a length of about 35 mm. Therefore, it is hard to provide a small straight bore (for example, 1.5 mm diameter) for the core 13 from a processing technical point of view.
The ejecting pin 16 pushes the moulded shutter 7 at an inner wall surface of the connecting member 10 thereof to remove it from the core 13. As a result, a part of the connecting member 10 projects outwards or a moulding flash projects inwards from the inner wall surface of the connecting member 10. These projections will deteriorate the slidability of the shutter 7.
In order to overcome the problems pertaining to such projections, it is preferable to take a long time to cool the mouldings (shutters 7) and to eject them after complete curing thereof. However, accordingly the total time period for the moulding operation (moulding cycle) is prolonged.
As described above, the slide movement of the shutter 7 is limited by the stepped parts of the recess portions 6 of the casing 1. However, if the side plates 9a and 9b of the shutter 7 extend apart from each other to widen an opening end A, the shutter 7 can slide beyond the stepped part (FIG. 25). Therefore, the hole 8 will not align with the windows 5 thus preventing the head from entering into the windows 5.
Even though the side plates 9a and 9b extend parallel to each other on the moulding operation, repeated usage of the shutter 7 causes that the side plates 9a and 9b to spread apart from each other to widen the opening end A, as shown in FIG. 25. Further, the widened opening end A abuts against an insert slit of the disk driving apparatus to prevent it from entering into the slit.
Furthermore, if the side plates 9a and 9b are moulded to extend too close to each other to produce a narrow opening A, sliding resistance between the shutter 7 and the recess portion 6 becomes so large as to deteriorate the slidability of the shutter 7 (FIG. 26).
A conventional shutter is formed to be of a U-shaped cross section by bending a thin metal plate, for example, a stainless steel plate of a thickness of 0.2 mm. However, it is difficult from the bending process to obtain a higher accuracy in the dimension of the shutter. Further, the metal shutter may readily shave down the synthetic resin casing and may be readily detached from the casing on impact if dropped. For these reasons, it is proposed that the shutter be formed integrally by means of injection moulding of a synthetic resin.
The moulds used in the injection moulding are so arranged, as shown in FIG. 27, that a core 13 is supported at opposite sides thereof by side slide moulds 12 and 12 to define a longitudinal cavity for the shutter, and a stationary mould 11 is mounted on these moulds.
In this arrangement, the supporting force for the core 13 is one perpendicular to the clamping force for clamping these moulds. Namely, such a supporting force is one transmitted through locking blocks and an angular pin and is not sufficient to withstand the injection pressure. During the moulding, if resin is not injected simultaneously into the cavity at both sides of the core 13, the injection pressure of resin at the one side of the core 13 into which resin is injected, at first urges the core 13 towards the other side to become one side plate thick. Accordingly, the other side plate will become thinner and thinner.
As shown in FIG. 28, a cartridge casing 1 of a magnetic disk cartridge to which a conventional synthetic resin shutter 7 is mounted is provided with a recess 17. A pin 18 of a recording/reproducing apparatus enters into the recess 17 to abut against an edge of the shutter 7 and moves it from a closed position (shown in the drawings) to an open position in a direction X to open the hole 8.
For the moulding of such shutter 7, a gate is disposed at an edge of the connecting member 10 adjacent to the hole 8. Therefore, after the moulding, a tapered gate mark 19 is left at the edge of the connecting member 10 to extend towards the recess 17.
The gate mark 19 prevents the pin 18 from engaging with the shutter 7 and may ride on the side plates 9a or 9b of the shutter 7. It becomes impossible to obtain a reliability of the movement of the shutter 7.